The Aznalcóllar dyke failed and released much of its stored, saturated pyritic tailings after a process of progressive failure in the foundation clay. 1.5 Mm3 of tailings and 5.5 Mm3 of acidic water were rapidly discharged from the pond. The paper reviews the main geotechnical aspects that contributed to the development of a sliding surface under the dyke: its downward construction procedure, the brittle nature of the over-consolidated, high plasticity foundation clay, and the prevalent high pore pressures in the clay. The downward construction method created a “wave” of high stress ratios under the advancing toe of the dyke capable of taking the strength from peak to residual values. The brittleness of the foundation clay is very significant because of its high plasticity and the presence of montmorillonite among its mineralogical constituents. The high pore pressures are a consequence of the high density tailings (3.1 g/cc), the low permeability of the clay, and the consolidation process in a dominant upward direction. Also discussed in the paper are the dynamics of the dam failure (displacement, velocity, and acceleration). The geometry of the dyke, in plan view, and its relationship with the direction and dip of the clay layers explains the position of the failure. This paper summarizes the lessons derived from this case history.

中文翻译：

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西班牙西南部 Aznalcóllar 尾矿坝的故障

Aznalcóllar 堤坝在地基粘土中经历了渐进式破坏过程后，发生了故障并释放了大部分储存的饱和黄铁矿尾矿。1.5 Mm3 的尾矿和 5.5 Mm3 的酸性水从池塘中迅速排出。该论文回顾了导致堤坝下滑动面发展的主要岩土工程方面：其向下施工过程、过度固结的高塑性地基粘土的脆性以及粘土中普遍存在的高孔隙压力。向下的施工方法在能够将强度从峰值到剩余值的堤坝的前进趾部下创造了一个高应力比的“波浪”。基础粘土的脆性非常显着，因为它具有高可塑性，并且在其矿物成分中存在蒙脱石。高孔隙压力是高密度尾矿 (3.1 g/cc)、粘土的低渗透性以及占主导地位的向上方向的固结过程的结果。论文中还讨论了大坝破坏的动力学（位移、速度和加速度）。在平面图中，堤坝的几何形状及其与粘土层的方向和倾角的关系解释了破坏的位置。本文总结了从这个案例历史中得出的教训。它与粘土层的方向和倾角的关系解释了破坏的位置。本文总结了从这个案例历史中得出的教训。它与粘土层的方向和倾角的关系解释了破坏的位置。本文总结了从这个案例历史中得出的教训。